Pekka Pkk÷nen
Document: draft-paakkonen-addressing-htr-manet-00.txt Mika Rantonen
Expires: June 2004 Juhani Latvakoski
VTT Electronics
December 2003
IPv6 addressing in a heterogeneous MANET-network
draft-paakkonen-addressing-htr-manet-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document presents IPv6 addressing related to end-to-end
connectivity in a Mobile Ad hoc Network with heterogeneous nodes.
Internet connectivity for the mobile ad hoc network has to be provided
by an Access Router. The nodes in such a network could only have IPv6
functionality, or contain support for Mobile IPv6 (MIPv6) or facilitate
ad hoc routing by using a MANET-based routing protocol. End-to-end
connectivity means that the nodes must be able to communicate with each
other locally and over the Internet. The draft focuses on the Ad hoc
On-demand Distance Vector (AODV) as a MANET-based routing protocol.
Table of contents
Abstract i
1. Introduction i
2. Terminology 2
3. Terms 2
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4. IPv6/MIPv6 addressing 2
4.1. Functionality it the AR.......................................4
5. MANET-addressing 4
5.1. Duplicate Address Detection (DAD).............................4
5.2. Global connectivity...........................................5
5.3. Global vs. site-local addresses...............................5
5.3.1. AODV-MIPv6 co-operation.................................5
6. IPv6-MANET addressing 6
6.1. AODV communication algorithm..................................6
6.2. Address autoconfiguration and communication issues............6
7. NEMO addressing 8
8. Security issues 8
9. Open issues 8
References 9
Author's addresses 9
APPENDIX A IPv6/MIPv6 addressing example 10
A.1. Proxy Neighbor Discovery (PND) in the AR.....................10
A.2. Redirect ICMP message........................................11
APPENDIX B Global connectivity via next hop routing 11
Full Copyright Statement 13
1. Introduction
This document describes IPv6 addressing, which is related to the
end-to-end connectivity in a heterogeneous Mobile Ad hoc NETwork
(MANET). The heterogeneity means that the nodes in the MANET-network may
contain different capabilities, which has been illustrated in figure 1.
First of all nodes with only IPv6 functionality might be present. Also
Mobile IPv6 (MIPv6) [1] enabled nodes might be present, either MIPv6
Corresponding Nodes (MIPv6_CN) or MIPv6 Mobile Nodes (MIPv6_MN).
MIPv6_CNs have MIPv6 Route Optimization (RO) capability, but don't
support mobility [1]. MIPv6_MNs have MIPv6 mobility extensions [1].
These nodes are referred in this document to as IPv6/MIPv6-nodes. MANET
routing protocol supported nodes might also be present, which in
addition have similarly different capabilities as the IPv6/MIPv6-nodes
(IPv6/ MIPv6_CN/ MIPv6_MN). In this document Ad hoc On-demand Distance
Vector (AODV) routing protocol functionality has been focused on. The
nodes of the MANET-network have to be able to communicate with each
other, and also with a Corresponding Node (CN) of the Internet
(end-to-end connectivity).
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CN HA_MN
| |
| |
_________|_________|________
\ /
\ Internet /---------HA_MR
\_____________________/
______________________|__________________________
( | )
( AR/MR --------MANETnode )
( / \ | | )
( / | \ | | )
( / | \ | | )
( / | \ | MANET )
( / | \ | node )
( / | \ | / )
( IPv6------MIPv6_CN---MIPv6_MN / )
( node )
( )
( Heterogeneous MANET- )
( network )
(_______________________________________________)
Figure 1. Heterogeneity in a hybrid MANET-network.
If the heterogeneous MANET-network needs global Internet connectivity,
it has to have one or more Access Routers (AR), which is/are connected
to the Internet. This AR is static if the MANET-network doesn't move
in relation to the Internet topology. Network Mobility might also be
supported as defined in the NEMO working group [2]. In this case the
ARs are considered as Mobile Routers (MR), which maintain Internet
connectivity by using bi-directional tunneling with their corresponding
Home Agent (HA), when the mobile network is away from home.
IPv6 addressing related to IPv6/MIPv6-nodes can be referred
to as IPv6/MIPv6-addressing, and IPv6 addressing related to MANET-nodes
MANET-addressing. IPv6-MANET addressing comprises communication between
IPv6/MIPv6-nodes and MANET-nodes. The heterogeneous nodes of the
mobile ad hoc network should also be able to communicate with a
Corresponding Node (CN) of the Internet outside of the MANET-network,
which can be referred to as global communication. The CN might also be
an IPv6-node, a MIPv6_CN or a MIPv6_MN. End-to-end connectivity in a
heterogeneous MANET-network consists of the different local and global
communication use cases between the heterogeneous nodes. This document
describes the IPv6 addressing related to end-to-end connectivity in
such a heterogeneous multi-hop MANET-network.
The structure of the document is as follows:
Chapter 3 describes terms used in the document. The next three chapters
deal with the IPv6 addressing related to the heterogeneous
MANET-network. NEMO addressing is focused on in chapter 7. Chapter
8 discusses security issues, and chapter 9 presents issues for further
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development.
2. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3].
3. Terms
This document uses mobility related terms as defined in [15], and
network mobility related terms as defined in [16]. In addition the
following terms are used:
Access Router (AR)
AR provides IP connectivity for the nodes by default routing, and
acts as an Internet gateway. The AR could also be considered as a
Mobile Router (MR) if network mobility is supported by it.
Flat Routing
Flat routing considers the ad hoc network without subnet partitioning
Hierarchical Routing
The ad hoc network is considered as logically separated subnets.
IPv6-node
Node with plain IPv6 functionality [1]. Could also be considered
as a Fixed Node (FN), because an IPv6-node doesn't support mobility.
Mobile IPv6 Corresponding Node (MIPv6_CN)
Mobile IPv6 node with Route Optimization capabilities as defined
in [1].
Mobile IPv6 Mobile Node (MIPv6_MN)
Mobile IPv6 node with mobility support as defined in [1].
4. IPv6/MIPv6 addressing
The IPv6/MIPv6 nodes configure a link-local address which may be used
only if the destination is on a local link. Global addresses are needed
if the nodes need to communicate over the local link or over the
Internet. Either stateless [4] or stateful [5] address
autoconfiguration could be used for global address generation. In this
document stateless address autoconfiguration has been focused on.
In case of stateless address autoconfiguration, the AR sends Router
Advertisements (RA), and includes an IPv6 prefix to the Prefix
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Information -option [6], which the IPv6/MIPv6-nodes attach to the
interface-ID to create a global IPv6 address [7]. To enable default
routing for the nodes, the Router Lifetime field of the Router
Advertisement (RA) MUST be non-zero [6]. When the nodes receive a RA
with a non-zero Router Lifetime field, an entry is added to the default
router list [6]. (Implementation note: Some platforms create a Routing
Table (RT) entry for the AR's link-local address (::/0 -> AR's
link-local address) ). If the Router Lifetime would be zero, default
routing would be disabled, and outside communication with a CN of the
Internet would not be possible.
The IPv6 prefix is advertised as ON-link by setting the L-flag in the
Prefix Information -option of the RA [6]. When a IPv6/MIPv6-node
considers the IPv6 prefix to be ON-link, it sends the packets for the
destination to the interface. (Implementation note: On some platforms
an RT entry is created for the IPv6 prefix towards the interface of the
AR (IPv6 prefix -> ethx) ). The ON-link prefix causes the IPv6/MIPv6-
nodes to send packets to the interface for destinations, which have
configured an IPv6 address from the IPv6 prefix (local destinations).
If the L-flag is not set, it "conveys no information concerning
on-link determination and MUST NOT be interpreted to mean that
addresses covered by the prefix are off-link" [6]. This causes the
IPv6/MIPv6-nodes to use the default router for all destinations. For
clarity in this document the ON-link model is used, when the L-flag is
set, and the OFF-link model is used, when the L-flag is not set.
Figure 2 describes an example of a situation in which the AR
advertises an IPv6 Prefix, with a Router Lifetime of 5000 in the ON-link
addressing model. It causes the IPv6/MIPv6-node to add entries for the
default router and IPv6 prefix to the Routing Table (RT). In the example
the default router list has been implemented by using the RT.
AR
|
|
| Router Advertisement
| || Router Lifetime = 5000
| || Prefix Information Option
| \ / L-flag = 1
| \/ A-flag = 1
| Prefix = IPv6 Prefix
| Source Link-layer Address Option
| Link-layer address of AR
|
IPv6/MIPv6-node
RT: ::/0 -> AR's link-local address
IPv6 Prefix -> ethx
Figure 2. Stateless address autoconfiguration.
When the AR advertises the IPv6 prefix with the ON-link model, it causes
the communicating nodes to send packets directly to each other (to the
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interface). The ON-link addressing model might be a problem with certain
access technologies. For example consider a case when IEEE 802.11b
Wireless LAN (WLAN) is used in the ad-hoc mode, and the IPv6/MIPv6 nodes
communicate locally on the same link. If the global addresses are used,
communication isn't possible if the nodes are positioned in such a way
in which the nodes are not on each other's WLAN communication range.
This is caused by the distance between the nodes (direct radio
connectivity isn't possible), when the nodes send packets directly to
each other (to the interface). The communication could however be
enabled by advertising the IPv6 prefix as OFF-link or by executing Proxy
Neighbor Discovery in the AR, if the AR is spatially positioned in such
a way, that it is able to provide routing for the nodes (i.e. AR is in
the radio communication range of both nodes). This would route the
packets via the AR. In this particular case, routing via the AR is also
the downside of the OFF-link model, when the peers are in the radio
communication range of each other (unoptimal routing). Specific details
on how the ON-link addressing model, Proxy Neighbor Discovery (PND) and
Redirect ICMP messages relate to the ad hoc mode of WLAN are described
in Appendix A.
4.1. Functionality in the AR
The access technology used and the network topology of the Access
Network SHOULD be taken into account when making the choice of the
ON-link addressing model of the IPv6 prefix in the AR. As described in
appendix A the OFF-link model could be used for WLAN environments which
use the ad-hoc mode (if the PND function is not used in the AR in the
ON-link model). But if the WLAN infrastructure mode with access points
would be used the choice of the addressing model could be different.
The PND function MAY be executed with the ON-link model with some
access technologies as described in appendix A.
The access technology SHOULD also be taken into account, when making
the choice of enabling/disabling Redirect ICMP message sending in the
AR. As described in appendix A the sending of Redirect-ICMP messages
MAY be disabled in the AR, when WLAN is used in the ad-hoc mode.
5. MANET-addressing
The MANET-nodes configure a MANET-address, which is used for
communication. Either a site-local or global address could be
configured (although the use of the site-local address has been
deprecated by the IETF [8]). To create a unique MANET-address,
Duplicate Address Detection (DAD) must be used.
5.1. Duplicate Address Detection (DAD)
The main purpose of the DAD procedure is to guarantee the uniqueness of
the IPv6 address to be used in the MANET. The uniqueness test messages
(Address Request (AREQ), Address Reply (AREP)) have to disseminate over
the MANET. The DAD described in [9] could be used, and the DAD could
also be improved as described in [10]. The latter solution performs the
DAD only on the interface-ID part of the MANET-address to be created,
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and also reduces the unnecessary forwarding of the AREQ-message.
5.2. Global connectivity
To enable global connectivity for a MANET-node, the MANET-node must have
a globally unique address, the packets from the Internet must be
routable to the MANET-node, and the MANET-node must be able to send
packets to the Internet. The MANET-nodes have to configure a global
MANET-address by acquiring an IPv6 prefix from the AR, which is attached
to the interface-ID of the node. This functionality could be achieved as
described in [11]. In this case the nodes configure three routing table
entries to enable global routing (default-route/0 -> AR; AR -> next-hop
towards AR; next-hop -> ethx). Appendix B describes how global
connectivity could be achieved via next-hop routing by using a reactive
MANET-protocol (AODV). In this case only two routing table entries are
needed (default-route/0 -> next-hop; next-hop -> ethx).
5.3. Global vs. site-local addresses
When the AODV-nodes communicate with each other, route discovery for
on-demand routing protocols are used as described in [12]. This means
that the route is discovered on-demand based on the current ad hoc
network topology.
The MANET-node may use either a site-local address or a global address
configured via IPv6 prefix discovery as a MANET-address, which means
that both addresses cannot be used at the same time. If the site-local
address is used as a MANET-address, Internet communication is not
possible, because packets with a site-local source address cannot be
routed to the Internet. This means also that it is not possible to
communicate with local MANET-nodes, which are away from home and use
the home address as the source address for local communication.
The site-local address can be used in multiple sites and the address
itself doesn't contain an indication about a particular site. This kind
of ambiguousness presents problems to the application developers and
multi-sited routers. This has led the IETF to deprecating the use of
site-local address [8], and search for alternative solutions [13]. This
discourages further the use of site-local addresses instead of global
addresses. It remains to be seen how the alternative addressing solution
can be used with AODV [13].
5.3.1. AODV-MIPv6 co-operation
A typical way for a MIPv6_MN to choose a default router and configure a
COA is to receive RAs sent by the AR. If AODV is used as a MANET-routing
protocol, the default router and COA are configured via a
reactive IPv6 Prefix discovery sequence. It is desirable for an AODV
supported MIPv6_MN to use its home address when at home, and its COA
when away from home to avoid unnecessary tunneling. To enable this, the
choice of being in the home or foreign network should be done after the
IPv6 Prefix discovery sequence by comparing the received IPv6 Prefix to
the home network prefix similarly as the IPv6 prefixes advertised with
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RAs are used for movement detection in standard MIPv6 networks.
If the home network prefix is equal to the IPv6 Prefix, the MIPv6_MN
uses the configured address as its home address and refreshes the route
for it. Otherwise the address is used as a COA, which is registered
after the route refresh sequence to the HA of the MIPv6_MN. If the
MIPv6_MN moves away from the home MANET-network, and continues to use
the configured MANET-address as its home address, its HA has to defend
the home address by answering to AODV's DAD messages, so that no other
node can configure the same address in the MANET-network. This
functionality should be similar as the standard MIPv6 home address
defending at the HA [1].
6. IPv6-MANET addressing
The MANET-nodes should be able to communicate with local IPv6/MIPv6-
nodes and CNs in the Internet. This chapter describes IPv6 addressing
issues related to such use cases.
6.1. AODV communication algorithm
The following communication algorithm supports hierarchical routing
for COAs and flat routing for site-local addresses:
1. If the destination is a site-local MANET-address or the destination's
IPv6-prefix is equal with the IPv6 Prefix received via IPv6 Prefix
Discovery => execute route discovery
2. Otherwise send packets via the default router
The flat routing approach has to be used for the site-local addresses,
because site-local addresses don't contain any information about a
specific subnet. The need for route discovery to COAs prior to
communication is based on the IPv6 Prefix. In this case the packets
between multiple MANETs using COAs would flow via the ARs of the
different MANETs.
In [11] it has been defined that the MANET-node MAY use route discovery
always when sending packets whether or not the destination is in the
Internet or not. If in this case the CN is in the Internet and no answer
to the RREQ is received, the CN is deduced to be outside the MANET, and
the default router is used. The algorithm presented in this document
uses the default router immediately, when packets are sent to local
IPv6/MIPv6-nodes or CNs in the Internet. This means that the initial
route discovery phase is not needed, which results in faster
communication initiation with the peer compared to the solution
presented in [11]. There is also no need to add destination entries to
the routing table via the default router, (destination ->
default-router) which are needed, if route discovery is used always
when initiating communication with a random node at the first time.
6.2. Address autoconfiguration and communication issues
IPv6/MIPv6-node related DAD guarantees that the interface-ID of the
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IPv6-address is unique on a link [4]. The IPv6/MIPv6-nodes discover
the IPv6 prefix via the RAs sent by the AR, which is attached to the
interface-ID to configure a unique IPv6 address. Also a link-local
address is created by attaching a well-known link-local prefix
(fe80::/64) to the interface-ID [4][7]. MANET-address related DAD
guarantees that the interface-ID is unique in the MANET [10]. The IPv6
prefix used in the MANET is received via IPv6 Prefix discovery, which
is attached to the MANET related interface-ID to create a unique IPv6
address.
It is possible that equal interface-IDs are configured in a
heterogeneous MANET-network, because the scope of the DAD-procedures
related to the interface-IDs overlap. To guarantee unique global IPv6
addresses, the IPv6 prefixes used in the different autoconfiguration
procedures have to be different.
End-to-end connectivity between heterogeneous nodes is described in
figure 3. Because the IPv6 prefixes have to be different, it doesn't
matter which addressing model is used with the IPv6-MANET communication.
Also PND is not required in the AR, because the IPv6-MIPv6-nodes send
always packets for the MANET-node via its configured default router
(::/0 -> AR's link-local address). The MANET-node also uses its
configured default router for communication with the IPv6/MIPv6-node
(::/0 -> next hop towards MR) without using the route discovery
procedure, because the IPv6 prefixes are different. Global addresses
have to be used always when the default router is used, in case the CN
would be in the Internet instead of being in a local IPv6/MIPv6-node. If
the IPv6/MIPv6-node and MANET-node are on the same link and in the radio
communication range of each other, the only possible way for these nodes
to communicate directly with each other is by using link-local addresses
, because the default router is used in other situations for routing
between the nodes.
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CN HA_MN
| |
| |
_________|_________|________
\ /
\ Internet /---------HA_MR
\_____________________/
___________________|____________________________________
( | )
( AR/MR RT: IPv6-prefix -> ethx )
( /\ /\ MANET1-node -> ethx )
( / \ MANET2-node -> MANET1-node)
( / MANET1-node )
( / \ RT: ::/0 -> AR )
( / \ MANET2 -> ethx )
( \/ \/ )
( IPv6/MIPv6<----------->MANET2-node )
( node link-local )
( addresses )
( RT: ::/0 -> AR RT: ::/0 -> next-hop )
( towards AR )
(___________________________________next-hop -> ethx_____)
Figure 3. End-to-end connectivity in a MANET-network with heterogeneous
nodes.
If the AR sends Redirect ICMP-messages and the AODV-node and NEMO-node
are on the same link, the Redirect-messages cause the same problem,
which is present in IPv6/MIPv6-communication, but only for communication
from the IPv6/MIPv6-node to the AODV-node.
7. NEMO addressing
As mentioned before the AR could also be a MR, which would make the
heterogeneous MANET-network mobile. In this case the NEMO bi-directional
tunneling used on the MR's egress interface is transparent to the
end-to-end connectivity of the nodes in the MANET-network, because
seamless mobility is supported by the NEMO-approach i.e. the IP
addresses configured for the nodes of the mobile network don't change
when the network moves.
In any case the AR/MR needs two IPv6 prefixes for the autoconfiguration
of both MANET and IPv6/MIPv6-nodes. These prefixes have to be either
statically configured for the AR/MR, or delegated dynamically from some
network entity for example via DHCPv6 [5] [14].
8. Security issues
Security issues have not been considered in this document, but should be
taken into account in a future version of this document.
9. Open issues
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The source address selection of a node in the MANET-network is an issue
for further work. For example when a MIPv6_MN communicates with a local
IPv6-node, the COAs should be used for communication to avoid tunneling
via the HA_MN (instead of using home addresses). Security issues should
also be taken into account in the future.
References
[1] D. B. Johnson, C. E. Perkins, J. Arkko "Mobility Support in IPv6"
<draft-ietf-mobileip-ipv6-24.txt>, Internet Draft, June 2003.
[2] NEtwork MObility working group website URL:
http://www.ietf.org/html.charters/nemo-charter.html.
[3] S. Bradner "Key words for use in RFCs to Indicate Requirement
Levels" BCP 14, RFC 2119, March 1997.
[4] S. Thomson and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[5] R. Droms et al. "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[6] T. Narten, E. Nordmark and W. Simpson, "Neighbor Discovery for IP
Version 6 (IPv6)", RFC 2461, December 1998.
[7] R. Hinden, S. Deering "IP Version 6 Addressing Architecture"
<draft-ietf-ipv6-addr-arch-v4-00.txt>, Internet Draft October 2003.
[8] C. Huitema, B. Carpenter "Deprecating Site Local Addresses"
<draft-ietf-ipv6-deprecate-site-local-02.txt>, Internet Draft,
November 2003.
[9] C.E. Perkins et al. "IP Address Autoconfiguration for Ad Hoc
Networks" <draft-ietf-manet-autoconf-01.txt>, Internet draft,
November 2001.
[10] M. Rantonen, J. Keisala "IP Address Autoconfiguration with DAD
minimization for Ad Hoc Networks"
<draft-rantonen-manet-idaddress-dad-adhocnet-00.txt>, Internet
draft, August 2003.
[11] R. Wakikawa et al. "Global Connectivity for IPv6 Mobile Ad Hoc
Networks" <draft-wakikawa-manet-globalv6-02.txt> Internet draft,
November 2002.
[12] C.E. Perkins, E.M. Belding Royer, S. Das "Ad hoc On-Demand
Distance Vector (AODV) Routing" RFC 3561.
[13] R. Hinden, B. Haberman "Unique Local IPv6 Unicast Addresses"
<draft-ietf-ipv6-unique-local-addr-01.txt>, Internet draft,
September 2003.
[14] R. Droms "DHCPv6 Prefix Delegation for NEMO"
<draft-droms-nemo-dhcpv6-pd-00.txt>, Internet draft, June 2003.
[15] J. Manner, M. Kojo "Mobility Related Terminology"
<draft-ietf-seamoby-mobility-terminology-04.txt>, Internet draft
April 2003.
[16] T. Ernst, H. Lach "Network Mobility Support Terminology"
<draft-ietf-nemo-terminology-00.txt>, Internet draft, May 2003.
Author's addresses
Pekka Pkk÷nen
VTT Technical Research Centre Of Finland (VTT Electronics)
Kaitovyl 1
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90571 Oulu
Finland
email: pekka.paakkonen@vtt.fi
Mika Rantonen
VTT Technical Research Centre Of Finland (VTT Electronics)
Kaitovyl 1
90571 Oulu
Finland
email: mika.rantonen@vtt.fi
Juhani Latvakoski
VTT Technical Research Centre Of Finland (VTT Electronics)
Kaitovyl 1
90571 Oulu
Finland
email: juhani.latvakoski@vtt.fi
Appendix A: IPv6/MIPv6 addressing example
This appendix describes how Proxy Neighbor Discovery and Redirect ICMP
messages are related to the ad-hoc mode of the IEEE WLAN 802.11b access
technology.
A.1. Proxy Neighbor Discovery (PND) in the AR
PND MAY be used with certain access technologies, when the ON-link
addressing model is used in the AR. Figure 4 describes a situation,
in which the peers cannot communicate directly with each other, but the
AR is able to provide routing for the nodes (the circles represent the
wireless communication ranges of the nodes). The PND function means that
the AR answers on behalf of the destination with a Neighbor Advertisement
(NA) to the Neighbor Solicitation (NS) message sent by the source
(steps 1 and 2). The NA contains the link-layer address of the AR instead
of the destination. This causes the source to send packets for the
destination to the AR, which routes the packets to the final destination
(steps 3 and 4). This means that the AR accepts packets not explicitly
addressed to it. In the NA sent by the AR the Override-flag is set to
zero, so that the NA sent by the real destination with the Override-flag
set overrides the NA sent by the AR. This feature causes the source to
send packets to the real destination when the peers are within each
other's communication range.
________________________________________________________________
( [ ) ]
( [ ) ]
( 4. IPv6 packet [ ) 1.NS 3.IPv6 packet ]
( |-----------------------[---AR<--)----------------------| ]
( \/ [ | ) | ]
( Node2 [ |---)------------------->Node1 ]
(___________________________[________) 2.NA ]
[____________________________________]
Figure 4. Proxy Neighbor Discovery (PND).
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Consider the local mobility of the nodes in figure 4. The nodes may be
mobile in such a way that they may or may not be in each other's
communication range during a UDP/TCP session. In this case the IP
addresses don't change, because only one AR is present which sends RAs.
Reachability of the neighbor (destination) is dependent on the upper
layer information and Neighbor Unreachability Detection (NUD) as defined
in [6].
A downside of the PND function is that the AR has to know the IP and
link-layer addresses of the peers. Also security problems are present,
because a malicious AR might execute PND for the destination. The
advantage of the PND in the ON-link addressing model is that the
traffic between the local nodes are sent directly between the nodes,
when the nodes are in each other's communication range. In the
OFF-link addressing model the traffic would always goes via the AR.
A.2. Redirect ICMP message
Another thing related to some access technologies is the sending of the
Redirect ICMP-messages. When the source sends packets via the AR to the
destination, the AR discovers that the destination is in fact on the
same link as the source, and sends a Redirect ICMP message to the
source. The Redirect-message contains the link-layer address of the
destination, which causes the source to send packets to the real
destination instead of the routing via the AR, because the source
updates the link-layer address of the destination's IP address in the
neighbor cache [6]. If the peers are not within the radio communication
range of each other (figure 4) and the AR routes the packets between the
peers, communication ceases between the peers. This situation occurs
when the IPv6 prefix is advertised as OFF-link or the PND function is
used with the ON-link model in the AR. Figure 5 describes a situation in
which the AR sends a Redirect-message with the destination's
link-layer-address (LL-address), which causes the source to update its
neighbor cache.
AR-----Destination
|
|
| || Redirect ICMP-message
| || Target link-layer address
| \ / Destination's LL-address
| \/
|
IPv6/MIPv6-node
Neighbor cache: IPv6 address -> AR's LL-address/
Destination's
LL-address
Figure 5. Redirect ICMP messages.
Appendix B: Global connectivity via next-hop routing
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This appendix describes how global connectivity could be achieved with
AODV by using next-hop routing, and is similar to the one described in
[11]. This mechanism has been tested in a testbed and has been
described in figure 6.
AR
/|\ RT: Int.node -> eth0
1.RREQ (I-flag set) | 5. AODV-node -> Int.node
2.RREP (I-flag set) |
4.RREQ |
6.RREP |
\|/
Int.node RT: 5.AODV-node -> eth0
/|\ 3.MR ->eth0
1.RREQ (I-flag set) | 3.::/0 -> AR
2.RREP (I-flag set) |
4.RREQ |
6.RREP |
\|/ RT: 3. AR -> Int.node
AODV-node 3. ::/0 -> Int.node
Int.node -> eth0
Figure 6. Global connectivity via next-hop routing.
The global connectivity is enabled with IPv6 prefix discovery
(steps 1-3) and route refresh sequences (steps 4-6). IPv6 prefix
discovery is used for the address autoconfiguration purposes to enable
global connectivity for the AODV-node, and the route refresh procedure
maintains AODV-node reachability from the AR i.e. from the Internet.
The IPv6 Prefix discovery sequence begins when the AODV-node sends a
RREQ with the I-flag set to the ALL_MANET_GW_MCAST-multicast address
[11] from its configured site-local MANET-address (step1 in figure 6).
The site-local addresses's uniqueness has been tested in the DAD
procedure. The AR returns the IPv6 Prefix by sending a RREP with the
I-flag set to the AODV-node's MANET-address (step2). When the AODV-node
and intermediate nodes receive this RREP, a RT entry for the default
router and AR towards the next-hop towards the AR are created (step3).
The AR's address is a global address configured on the ingress interface
of the AR. After this the AODV-node attaches the IPv6 Prefix to the
interface-ID configured during the MANET-related DAD to create a unique
global IPv6 address. This enables global connectivity for the AODV-node.
In the route refresh sequence the AODV-node sends a RREQ to the default
router's address from its configured global IPv6 address (step4). The
default router's address is a global address configured on the ingress
interface of the AR. When the AR and intermediate nodes receive the
RREQ, they create an entry for the AODV-node's global address towards
the next-hop towards the AODV-node (step5). This enables AODV-node's
reachability from the Internet. Finally the AR sends a RREP in response
to the RREQ (step6). The AODV-node has to execute the route refresh
sequence in certain time periods in order to maintain reachability from
the AR [11]. If the route cannot be refreshed i.e. the AODV-node loses
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reachability to the AR, the AODV-node has to return to using the
site-local MANET-address, because the AR might not be present anymore to
provide default routing and the validity of the IPv6 prefix has expired.
In [11] it has been proposed to implement default routing via the global
address of the AR. In that kind of configuration the furthermost
AODV-node of figure 6 would require three RT entries (::/0 -> AR ;
AR -> next-hop towards AR ; next-hop -> ethx) for default routing. This
isn't implementable on the Linux platform, because the next-hop router
must have a RT entry towards the interface as described in figure 6.
This is the reason default routing had to be provided via a next-hop as
describes in this appendix.
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